The present invention relates to an electrophotographic image-forming process for using in a copying machine, laser printer or the like, a developer for using in the image-forming process, as well as an image-forming system.
Heretofore, a corona charger such as a corotron or scorotron has been used generally for charging a dielectric layer or the like of a latent image carrier (for example, a photoconductor) in an electrophotographic apparatus such as an electrophotographic copying machine or an electrophotographic printer. The corona charger requires a high voltage for charging the photoconductor and involves a drawback of generating a great amount-of ozone, thereby accelerating the deterioration of the photoconductor. In addition, an interest in the environmental protection is increasing in recent years and printers or the like other equipment are often used in a place near to a human body such as on a desk with proceeding in miniaturization and personal use of them. Therefore a charging device generating less amount of ozone which is toxic to a human body, has been demanded.
In view of the foregoing situation, a merit of contact charging such as Loller charging has been discovered and gradually put to practical use in recent years. The roller charging is a method of contacting the roller member obtained by coating a core such as a metal core with a conductive rubber or the like and forming into a roller-shape, with a photoconductor, and applying a voltage between the core of the roller and the photoconductor, thereby charging the surface of the photoconductor. The charging method has a merit capable of operating at a lower application voltage, enabling stable charging by superposing an alternating current voltage (refer to Japanese Patent Application Laid-Open (KOKAI) 63-149669(1988)) and generating less amount of ozone.
Further, in order to overcome the drawback in the contact charging method, that the surface of the photoconductor is liable to be damaged upon contact, a neighboring charging method for conducting charging making the surface of a charging member neighbor to a photoconductor may be considered.
However, when both of the two kinds of charging methods described above have been applied to a commercial copying laser printer to carry out a life test, it has been found that there occurs an additional problem to be solved.
That is, during repeating an image formation for a long time, toner particles or fine silica particles added as a fluidity improving agent are deposited, depending on the case, on the surface of a charging member to hinder uniform charging.
A blade cleaning method is used in a cleaning step of a transfer residual toner on a photoconductor of a copying machine/laser printer used for the experiment. The toner particles or fine silica particles are non completely scraped off by a cleaning blade and small amount of toner particles and fine silica particles remains on the surface of the photoconductor and then transfers from the surface of the photoconductor to the charging member. It is considered that the transferred toner particles and the fine silica particles are accumulated little by little to form an insulation layer on the surface of the charging member, during repeating the image formation, thereby failing to attain sufficient charge injection. In charging by the existent corotron or scorotron, such a problem can be coped with by merely cleaning the discharge wire periodically, since there has been a gap of greater than about 1 mm between the photoconductor and the transfer member, and the transfer of the toner particles and silica particles to the charging member is scarcely caused.